This revised application is for a NIA Geriatric Academic Award to foster the applicant's development as an independent and productive investigator in Gerontology in an academic environment. This epidemiological study will describe the clinical progression and test hypotheses on the pathophysiological mechanism for failure to thrive in a cohort of older adults following acute illness. Failure to thrive in older adults is a syndrome characterized by the progressive decline in physical function and ultimately death. The failure to thrive syndrome is common, often associated with acute illnesses in older adults, and has been understudied from an epidemiological and a pathophysiological perspective. Acute illness (community acquired pneumonia) will be used to identify a target population of older adults with a high prevalence for failure to thrive in this proposed project. Community acquired pneumonia is an acute illness from which healthy individuals should recover completely. Yet, 43% of patients with community acquired pneumonia die within 18 months, 18% experience functional decline by self report, and only 39% report "full recovery" (106). Older adults who have recovered from acute community acquired pneumonia will be prospectively examined after discharge from hospital at 2 and 6 weeks, 3, 6, 9, 12, 18, and 24 months with timed physical performance tests and biochemical studies. For this project a decline in physical functional performance (demonstrated by declining performance on timed tests) occurring during 2 years observation will be considered evidence for failure to thrive. Specific aims are: 1) To determine the prevalence of failure to thrive in this target population of older adults; 2) To describe the clinical progression of failure to thrive in this target population; 3) To test the hypothesis that subject characteristics are significant predictors and/or modulators of failure to thrive and mortality. Factors to be examined include: age, socioeconomic status, living arrangement, comorbid disease burden, dementia, depression, quality of life, strength, muscle mass, and serum measures of albumin, prealbumin, transferrin, retinol-binding protein, lipids, and blood cell count; and 4) To test the hypothesis that immune response, manifested as lymphocyte proliferative response, is impaired in subjects with failure to thrive and is associated with decreased serum concentration of insulin-like growth factor 1 (IGF-1). This project is designed to provide meaningful information on the understudied syndrome of failure to thrive in older adults.